1. Maintenance of a stable blood glucose concentration is important. Explain why.
Answer
To ensure that the substrate for respiration is readily available to cells and to maintain a constant water potential of blood.
2. What is the role of adrenaline in controlling blood glucose concentration ?
Answer
Adrenaline attaches to receptor on the surface of target cells. This causes enzymes to be activated in order to convert glycogen to glucose.
3. The figure below shows a diagram of the cells lining the Bowman's capsule and glomerulus. Identify the structures that are labelled.
Answer
4. A study was carried out to measure resting blood glucose concentrations in different groups of people. Before the study, all participants ate nothing and drank only water for 12 hours. Explain why this was necessary.
Answer
So blood glucose concentration was not the result of food or drink recently consumed.
5. The figure below shows the reabsorption and excretion rates of glucose in the kidney for different blood glucose concentrations. Describe how glucose is reabsorbed from the filtrate into the cells of the proximal convoluted tubule.
Answer
Glucose is reabsorbed by active transport. Up to a concentration of 180 mg per 100 cm3, all glucose is reabsorbed, meaning this process occurs against a concentration gradient.
6. Glucose is excreted into urine when the blood glucose concentration rises above 180 mg per 100 cm3. Explain why.
Answer
All glucose transporter proteins become saturated. As a result, the glucose concentration in the filtrate remains too high, and excess glucose cannot be reabsorbed, so it is excreted in the urine.
7. People who have high blood pressure may have protein present in their urine. Suggest a reason for this.
Answer
High blood pressure damages capillary walls/podocytes/basement membrane. Larger molecules such as proteins can pass through.
8. Diabetes mellitus is caused by a lack of insulin. People with this condition often have glucose present in their urine. They feel thirsty and need to urinate frequently. What is the cause of these symptoms ?
Answer
Feeling thirsty - High blood glucose lowers water potential of blood.
Needing to urinate frequently -
Glucose in urine lowers WP of filtrate. Less water reabsorbed from filtrate so urine volume greater.
9. A person with diabetes insipidus does not have glucose in their urine. Explain why.
Answer
People with diabetes insipidus have normal blood glucose concentrations, so all glucose is reabsorbed in the proximal convoluted tubule.